The present invention relates to a structure for attaching a fuel pump to a cylinder head of an engine. The fuel pump pressurizes fuel through, for example, rotation of an intake or exhaust camshaft and supplies the pressurized fuel to a pressure accumulation pipe of the engine.
FIGS. 11 and 12 show an example of this type of fuel pump attachment structure. The fuel pump attachment structure illustrated in the drawings includes an attachment base 71, which is formed integrally with and arranged on a metal cylinder head cover 13. A fuel pump 33 is received in a central hole 71a formed in the attachment base 71. A sealing member 34 is arranged between a flange 33a of the fuel pump 33 and the top surface of the attachment base 71. Bolts 35, which extend through the flange 33a and the sealing member 34, is each threadably received in a corresponding one of threaded holes 71b of the attachment base 71, thus attaching the fuel pump 33 to the cylinder head cover 13.
The fuel pump 33 has a pressurizing cylinder 36. A plunger 37 is received in the pressurizing cylinder 36. A tappet 37a is connected to the lower end of the plunger 37. A pump drive cam 38 is formed in an exhaust camshaft 21 at the position corresponding to the tappet 37a. As the pump drive cam 38 rotates integrally with the exhaust camshaft 21, the plunger 37 reciprocates in the upward-downward direction in the pressurizing cylinder 36. Through such reciprocation of the plunger 37, fuel in the fuel pump 33 is pressurized and supplied to a pressure accumulation pipe such as a common rail in the engine. After having been sent to the pressure accumulation pipe, the fuel is injected into a combustion chamber in the engine through a fuel injection valve.
In the fuel pump attachment structure shown in FIGS. 11 and 12, the cam 38 repeatedly applies great external force to the fuel pump 33. The cylinder head cover 13 thus must be formed of metal such as iron or aluminum alloy, and the weight of the engine is increased.
Japanese Laid-Open Patent Publication No. 2000-291503 discloses a fuel pump attachment structure described below. Specifically, a metal bracket is mounted on a cylinder head in a manner covered by a cylinder head cover formed of synthetic resin. A fuel pump is attached to and supported by the bracket. When the fuel pump is driven by a pump drive cam, the cylinder head cover does not receive great external force. The weight of the cylinder head cover can thus be reduced. However, the fuel pump attachment structure of Japanese Laid-Open Patent Publication No. 2000-291503 has two problems as will be described below.
The first problem is that there is not sufficient space for installing the bracket between the cylinder head cover and the cylinder head. This makes it difficult to mount the bracket on the cylinder head or to attach the fuel pump to the bracket. To avoid this problem, the fuel pump may be attached to and supported by the cylinder head cover instead of the bracket. However, in this case, the cylinder head cover, which is formed of synthetic resin, must be reinforced. This may bring about an additional problem. The second problem is that, since the bracket is received between the cylinder head cover and the cylinder head, a great number of bolts must be employed to fix the cylinder head cover and the bracket to the top surface of the cylinder head. This also complicates operation for attaching the fuel pump.